A leading cause of death in the United States and the world today is coronary artery disease, in which atherosclerotic plaque causes blockages in the coronary arteries, resulting in ischemia of the heart (i.e., inadequate blood flow to the myocardium). The disease manifests itself as chest pain or angina. In 1996, approximately 7 million people suffered from angina in the United States.
Coronary artery bypass grafting (CABG), in which the patient's chest is surgically opened and an obstructed artery is replaced with a native artery harvested elsewhere or a synthetic graft, has been the conventional treatment for coronary artery disease for the last thirty years. Bypass surgery typically requires that the patient be placed on cardiopulmonary bypass, in which the heart is stopped. In many cases, during resuscitation of the heart, the electrical activity within the heart will become erratic, a condition known as "fibrillation." Fibrillation may arise for no apparent reason, and results in ineffectual or out-of-sequence contractions of the heart, which--if not corrected--may be fatal.
Cardiac fibrillation is often brought under control by the application of electrical stimulus using previously known cardiac defibrillators, or by massaging the muscle. These devices pass a mild shock through the heart muscle, and encourage the heart to begin beating again with a normal rhythm. A certain number of cases, however, prove refractory to electrical stimuli, with consequent mortality. Thus, even though bypass surgery may have proceeded without difficulty, a patient might nevertheless expire if the his heart begins fibrillating in a manner that cannot be relieved using previously known electrical defibrillation apparatus or cardiac compression.
Another technique for treating patients suffering from cardiac ischemia is referred to as transmyocardial revascularization (TMR). In this method, a series of channels are formed in the left ventricular wall of the heart. These channels may be transmural (i.e., from the epicardium to the endocardium), or only partial (for example, from the endocardium and terminating in the myocardium).
Typically, between 15 and 50 channels about 1 mm in diameter and up to 3.0 cm deep are formed with a laser in the wall of the left ventricle to perfuse the heart muscle with blood coming directly from the inside of the left ventricle, rather than from the coronary arteries. It has also been proposed that the formation of such channels stimulates the creation of small blood vessels within the myocardium. Apparatus and methods have been proposed to create these channels both percutaneously and intraoperatively (i.e., with the chest opened).
An article entitled "Multiple Transmyocardial Puncture Revascularization in Refractory Fibrillation Due To Myocardial Ischemia", Ann. Thor. Surg., Vol. 6, No. 6, pp. 557-563 (1968), by M. D. White and J. E. Hershey, describes a case in which an effective beat was restored in a fibrillating heart by repeatedly puncturing the heart with an intravenous cannula. It was observed that when 100 punctures were made in a fibrillating heart, coupled with cardiac compression, electrical activity was restored to normal.
The approach presented in the foregoing article neither recognized nor addressed the risks of embolization that could occur as a consequence of ejecting material into the left ventricle with the intravenous cannula. Moreover, with advancements in TMR technology, and in particular, the dominance of laser technology as the preferred form of performing TMR, the potential for using TMR apparatus for defibrillation in acute cases has not been realized.
For example, U.S. Pat. Nos. 5,380,316 and 5,554,152 to Aita et al. describe intraoperative laser apparatus for forming channels extending from the epicardium to the endocardium. The laser includes an optical wave guide that is held against the patient's heart. Several pulses of the laser are required to form a transmural channel by ablation. U.S. Pat. No. 5,389,096 to Aita et al. describes a catheter-based laser system for performing TMR percutaneously, i.e., from within the left ventricle. U.S. Pat. No. 4,658,817 to Hardy describes a laser-based system for intraoperatively performing TMR that includes a needle portion for perforating an outer portion of the tissue, and a laser for ablating the inner portion. U.S. Pat. No. 5,591,159 to Taheri describes performing TMR using a catheter having an end effector formed from a plurality of spring-loaded needles.
None of the foregoing references recognize that TMR apparatus may have value in treating cardiac defibrillation that is refractory to electrical stimuli. Because laser-based systems, such as described in the Aita et al. patents, require costly and sophisticated technology, having such systems available to treat relatively infrequent cases of defibrillation refractory to electrical stimuli would be cost prohibitive. Moreover, laser-based systems do not provide for removal of ablated tissue, thus causing a risk of embolization by ablated tissue. Catheter-based systems, such as described in the Taheri patent, typically require to much set-up time to be of practical use in acute situations of defibrillation.
In view of the foregoing, it would be desirable to provide methods and apparatus for treating cardiac fibrillation refractory to electrical stimuli that uses relatively inexpensive components and which may be made readily available to the surgeon performing cardiac surgery.
It also would be desirable to provide methods and apparatus for treating cardiac fibrillation by forming transmural myocardial channels, and which aspirates tissue removed during the channel-forming process, thereby lessening the potential for embolization.
It would also be desirable to provide methods and apparatus for treating cardiac fibrillation wherein a portion used within a sterile field is disposable, thereby simplifying the sterilization process and reducing the cost of the system.